"We isolate the cells from the tooth," said Muotri. Through a program called the Tooth Fairy Project, he has convinced parents to send him their kids' baby teeth after they've fallen out. "It's completely non-invasive and it's an easy way to engage the families to participate in the science."

For a study published Tuesday in Molecular Psychiatry, Muotri and his colleagues extracted cells from the teeth of about 300 children. Then they reprogrammed tooth cells into brain cells using stem cell techniques.

When they put the brain cells derived from the teeth of autistic children under the microscope, they saw the hallmarks of autism: neurons of different sizes and shapes, and connection problems between brain cells.

But the genetics behind these physiological markers remain a mystery in many cases. To try to find mutations that could be leading to autism, Muotri sequenced the genomes of his research subjects. He was able to pinpoint a specific mutation underpinning one patient's brain features.

Muotri said, "Because we knew the gene, we were able to find one drug, called hyperforin." It's a compound that regulates the gene they'd identified. When they experimented with hyperforin on lab-grown neurons, the researchers saw promising results.

"By treating the neurons with this drug, we were able to revert them so they behaved like normal neurons," Muotri said.

Muotri admits this particular genetic mutation is probably not common among people with autism. But he says continuing to carry out studies like this can help personalize the understanding of autism down to each individual patient, and ultimately could help guide the search for broad autism therapies.